Olmsted,  P.£. 


on 


the 


physios!  properties 


of  -tvmb^r 


* :• 


’•)  ' -.V~- 


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CONTENTS. 


Page. 

Outline  of  timber-testing  work  in  Europe 533 

Outline  of  timber-testing  work  in  the  United  States 534 

Tests  in  the  Tenth  Census 534 

Tests  by  the  Department  of  Agriculture 534 

Tests  at  the  Massachusetts  Institute  of  Technology 535 

Miscellaneous  investigations 536 

Timber-testing  work  proposed  by  the  Department  of  Agriculture 536 

The  investigations  planned . 536 


ILLUSTRATIONS. 


Page. 

Plate  LXIX.  End  sections  of  beams  from  Longleaf  Pine,  photographed  before 

testing 536 

LXX.  Beams  from  Longleaf  Pine 536 


ii 


HILL 


TESTS  ON  THE  PHYSICAL  PROPERTIES  OF  TIMBER. 


By  F.  E.  Olmsted, 

Assistant  Forester , Bureau  of  Forestry. 
OUTLINE  OF  TIMBER-TESTING  WORK  IN  EUROPE. 


From  the  beginning  of  the  eighteenth  to  the  middle  of  the  present 
century  investigations  of  the  strength  of  wood  received  more  or  less 
attention,  principally  from  French  scientists.  Owing  to  the  limited 
scale  upon  which  the  work  was  done  and  to  the  rather  crude  methods 
employed,  the  results  were  necessarily  contradictory  and  unsatisfac- 
tory. In  1848  Chevandier  and  Wertheim  published  the  results  of 
tests  they  had  made  on  timber  of  the  Vosges  Mountains.  This  was 
the  first  case  in  which  a fairly  good  history  and  description  of  the 


test  material  was  given,  and  their  results  are  even  now  in  use. 

Most  of  the  modern  work  in  timber  testing  is  founded  on  that  of 
Dr.  H.  Ndrdlinger,  chief  forester  at  Hohenheim,  Wurttemberg.  The 
results  of  his  investigations  were  published  in  1860.  Among  the  most 


important  tests  of  recent  years  are  those  made  by  Bauschinger  and 


i 


published  at  Munich  in  1883  and  1887. 


These  tests  were  made  on 


3T Scotch  Pine  and  Spruce  from  the  Black  Forest,  and  special  attention 
was  given  to  the  conditions  under  which  the  timber  grew.  The  main 
object  of  the  work  was  to  determine  the  influence  of  forest  conditions 
and  the  time  of  felling  on  the  strength  of  the  wood.  In  the  publica- 
tion of  1883  the  following  statements  are  made,  modified  by  the  clause 
that  they  should  be  taken  as  a near  approach  to  the  truth  only : 


(1)  Stems  of  spruce  or  pine  which  are  of  the  same  age  at  equal  diameters,  and  in 
which  the  rate  of  growth  is  about  equal,  have  the  same  mechanical  properties 

4 (when  reduced  to  the  same  moisture  contents) , irrespective  of  local  conditions  of 
growth. 

(2)  Stems  of  spruce  or  pine  which  are  felled  in  winter  have,  when  tested  two 
or  three  months  after  the  felling,  about  25  per  cent  greater  strength  than  those 

I felled  in  summer,  other  conditions  being  the  same. 


Bauschinger,  in  his  publication  of  1887,  further  modifies  these  state- 
ments and  admits  that  a great  many  more  tests  must  be  made  in  order 
| to  prove  their  truth.  He  agrees  in  general  with  Hartig,  however,  that 
good  conditions  of  growth  produce  a good  quality  of  wood. 


533 


534  YEARBOOK  OF  THE  DEPARTMENT  OF  AGRICULTURE. 


OUTLINE  OF  TIMBER-TESTING  WORK  IN  THE  UNITED  STATES. 

Iii  America  the  most  extensive  work  in  timber  testing  lias  been  clone 
by  the  Division  of  Forestry  of  this  Department,  and  lw  Mr.  T.  P. 
Sharpies,  in  connection  with  the  Tenth  Census. 

TESTS  IN  THE  TENTH  CENSUS. 

The  tests  made  for  the  Tenth  Census  were  very  comprehensive,  and 
included  work  on  412  species;  they  were  not  intended,  however,  to 
be  of  practical  applicability  as  accurate  data  for  the  strength  of  the 
various  species.  As  Mr.  Sharpies  says,  “The  results  obtained  are 
highly  suggestive;  they  must  not,  however,  be  considered  conclusive, 
but  rather  valuable  as  indicating  what  lines  of  research  should  be 
followed  in  a more  thorough  study  of  this  subject.” 

TESTS  BY  THE  DEPARTMENT  OF  AGRICULTURE. 

The  timber  tests  made  by  the  Division  of  Forestry  of  this  Depart- 
ment were  begun  in  1891  and  interrupted  in  an  incomplete  state  in 
1896.  The  laboratory  work  was  carried  on  under  the  supervision  of 
Prof.  J.  B.  Johnson,  at  St.  Louis,  and  the  material  was  collected  from 
the  forest  itself  with  special  reference  to  the  conditions  under  which 
it  was  grown.  The  results,  therefore,  are  of  value  not  only  as  giving 
data  for  the  strength  value  of  various  woods,  but  also  as  indicating 
the  effect  of  different  conditions  of  locality  on  the  quality  of  the  tim- 
ber. The  tests  include  32  species,  with  308  trees,  furnishing  6,000 
test  pieces  and  material  for  over  45,000  tests;  20,000  pieces  were  used 
for  physical  examination,  to  determine  structure,  character  of  growth, 
specific  gravity,  moisture  conditions,  and  other  properties.  The 
principal  part  of  the  work  was  done  on  Southern  pines — Longleaf, 
Cuban,  Shortleaf,  and  Loblolly.  Tests  were  also  made  on  the  follow- 
ing species:  White  Pine,  Red  Pine,  Spruce  Pine,  Bald  Cypress,  White 
Cedar,  Douglas  Spruce,  White  Oak,  Overcup  Oak,  Post  Oak,  Cow 
Oak,  Red  Oak,  Texan  Oak,  Yellow  Oak,  Water  Oak,  Willow  Oak, 
Spanish  Oak,  Shagbark  Hickory,  Mockernut  Hickory,  Water  Hickory, 
Bitternut  Hickory,  Nutmeg  Hickory,  Pecan  Hickory,  Pignut  Hickory, 
White  Elm,  Cedar  Elm,  White  Ash,  Green  Ash,  and  Sweet  Gum.  Of 
these,  the  greatest  number  of  tests  were  made  on  Bald  Cypress,  White 
Oak,  Cow  Oak,  Overcup  Oak,  and  Spanish  Oak. 

Dr.  B.  E.  Fernow,  under  whose  direction  the  tests  were  made, 
makes  the  following  statement  in  regard  to  the  work: 

As  will  he  observed,  some  species,  like  the  Southern  pines,  have  been  more  fully 
investigated,  and  the  results  on  these  (published  in  Circular  12,  Division  of  For- 
estry) may  he  taken  as  authoritative.  With  those  species  of  which  only  a small 
number  of  trees  have  been  tested  this  can  be  claimed  only  within  limits  and  in 
proportion  to  the  number  of  tests. 

Data  arc  given  in  Circular  No.  15,  Division  of  Forestry,  for  all  t hese 
species  in  the  following  kinds  of  tests:  Compression  endwise,  bending 


TESTS  OF  THE  PHYSICAL  PROPERTIES  OF  TIMBER. 


535 


at  rupture,  bending  at  relative  elastic  limit,  compression  across  the 
grain,  and  shearing  with  the  grain.  The  results  obtained  are  in  all 
cases  reduced  to  12  per  cent  moisture  contents.  This  was  assumed  to 
be  the  “highest  average  moisture  contents  of  seasoned  wood.” 

Among  other  special  tests  the  following  were  made: 

(1)  Effect  of  “bleeding”  on  Longleaf  Pine.  The  results  indicated 
that  the  strength  was  not  affected. 

(2)  Influence  of  size  of  the  beams  on  strength.  The  results  indicated 
that  large  beams  “may  be  as  strong  as  the  small  sticks  cut  from 
them.”  . 

(3)  Influence  of  size  in  compression  members.  The  results  indicated 
“that  columns  may  be  as  strong  as  small  compression  pieces,  and 
when  weaker  the  presence  of  internal  defects  probably  accounts  for 
the  difference.” 

(4)  To  ascertain  the  effect  of  hot-air  treatment  in  dry  kilns.  “The 
results  indicate  no  detrimental  effect,  contrary  to  common  opinion.” 

TESTS  AT  THE  MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY. 

Prof.  G.  Lanza,  at  the  Massachusetts  Institute  of  Technology,  has 
done  a considerable  amount  of  tiinbentest  work,  and  in  1894  pub- 
lished his  results  in  Applied  Mechanics.  Tests  were  made  on  a 
limited  number  of  Yellow  Pine  and  White  Oak  columns  and  spruce 
pillars  and  compression  tests  on  WTiite  Pine  and  Yellow  Pine  posts. 
Transverse  tests  to  determine  the  breaking  load,  modulus  of  rupture, 
and  modulus  of  elasticity  were  made  on  beams  of  the  following  spe- 
cies: Yellow  Pine,  52  beams;  WTiite  Oak,  36;  White  Pine,  37;  Hem- 
lock, 17. 

In  addition,  a series  of  “time  tests”  were  made  on  spruce  and  Yel- 
low Pine;  the  weights  were  allowed  to  remain  on  the  beams  for  periods 
of  from  one  month  to  over  a year.  From  these  time  tests  Professor 
Lanza  draws  the  conclusion  that  “the  deflection  of  a timber  beam 
under  a long-continued  application  of  the  load  may  be  two  or  more 
times  that  assumed  when  the  load  was  first  applied.”  Professor 
Lanza  is  strongly  in  favor  of  using  sticks  of  merchantable  sizes  for 
testing  material  as  against  small  pieces.  In  regard  to  tests  on  small 
pieces  he  says : 

While  a great  deal  of  interesting  information  may  be  derived  from  such  tests 
as  to  some  of  the  properties  of  the  timber  tested,  nevertheless  such  specimens  do 
not  furnish  us  with  results  which  it  is  safe  to  use  in  practical  cases  where  full- 
size  pieces  are  used.  Inasmuch  as  these  small  pieces  are  necessarily  much  more 
perfect  (otherwise  they  would  not  be  considered  fit  for  testing),  having  less 
defects,  such  as  knots,  shakes,  etc.,  than  the  full-size  pieces,  they  have  also  a far 
greater  homogeneity.  They  also  season  much  more  quickly  and  uniformly  than 
full-size  pieces.  In  making  this  statement,  I am  only  urging  the  importance  of 
adopting  in  the  experimental  work  the  same  principle  that  the  physicist  recog- 
nizes in  all  his  work,  viz,  that  he  must  not  apply  the  results  to  cases  where  the 
conditions  are  essentially  different  from  those  he  has  tested. 


536  YEARBOOK  OF  THE  DEPARTMENT  OF  AGRICULTURE. 


MISCELLANEOUS  INVESTIGATIONS. 

Iii  addition  to  the  investigations  mentioned  above,  timber  tests  have 
been  made  on  a small  scale  in  various  parts  of  the  country,  but  owing 
to  lack  of  system  and  omission  of  important  details  they  have  but 
little  practical  value.  Tests  on  the  Southern  pines  are  in  a more 
complete  state  than  those  of  other  species,  but  it  may  be  stated  as  a 
whole  that  there  are  to-day  no  reliable  data  at  hand  on  the  strength 
of  the  principal  merchantable  timbers  of  the  United  States.  In  other 
words,  there  are  no  figures  on  the  strength  and  durability  of  Amer- 
ican woods  which  an  engineer  feels  fully  justified  in  applying  to  his 
practical  work. 

TIMBER-TESTING  WORK  PROPOSED  BY  THE  DEPARTMENT  OF 
AGRICULTURE. 

From  the  foregoing,  it  is  evident  that  there  is  an  urgent  need  for 
reliable  data  on  the  strength  of  American  timbers;  it  is  also  plain 
that  such  data  should  be  obtained  according  to  an  exhaustive  and 
systematic  plan.  Although  in  many  instances  wood  is  being  replaced 
by  metal,  the  former  will  alwayg  hold  an  important  place  as  a mate- 
rial for  constructive  and  other  purposes,  and  as  the  supply  of  timber 
diminishes,  as  it  is  rapidly  doing,  it  becomes  more  and  more  neces- 
sary to  determine  its  true  value,  so  that  it  may  be  used  to  the  great- 
est economic  advantage.  There  is  evidence  to  show  that  many  of 
the  species  which  are  now  classed  as  “inferior”  may  with  safet}^  take 
the  place  of  timbers  in  common  favor  at  the  present  time.  No  accu- 
rate data  whatsoever  exist  as  to  the  strength  of  timbers  of  the  Pacific 
slope ; and  as  these  are  becoming  more  and  more  important  and  will 
form  the  great  source  of  supply  in  the  future,  it  is  desirable  that 
their  strength  and  durability  be  accurately  determined  at  the  present 
time. 

THE  INVESTIGATIONS  PLANNED. 

The  Bureau  of  Forestry  of  the  Department  intends  to  resume  the 
work  of  timber  testing  and  to  conduct  the  tests  on  a large  scale,  in 
order  that  the  work  may  eventually  include  all  the  principal  species 
of  the  country.  The  aim  is  to  obtain  results  of  the  greatest  practical 
value  to  engineers  and  others  directly  interested  in  the  utilization  of 
timber.  The  work  will  be  divided  into  several  series,  as  follows: 

Series  I : Tests  oh  timber  collected  from  the  open  market. 

Series  II : Tests  on  timber  collected  from  the  forest. 

Series  III:  Tests  to  determine  the  effect  of  moisture  and  volatile 
oils  on  the  strength  of  timber. 

Series  IV : Tests  to  determine  the  effect  of  preservatives  on  the 
strength  and  durability  of  timber. 

Series  V : Tests  to  determine  the  effect  of  kiln-drying  methods. 


Yearbook  U.  S.  Dept,  of  Agriculture,  1902. 


Plate  LXIX 


End  Sections  of  Beams  from  Longleaf  Pine,  Photographed  Before  Testing. 


Yearbook  U.  S.  Dept,  of  Agriculture,  1902. 


Plate  LXX. 


Beams  from  Longleaf  Pine. 

[No.  1,  Large  timbers,  photographed  before  testing,  10  by  12  inches  by  16  feet;  No.  2,  break  in  a 
large  beam  after  cross-bending  test;  No.  3,  lines  of  rupture  in  small  beams  after  cross- 
bending test.] 


TESTS  OF  THE  PHYSICAL  PROPERTIES  OF  TIMBER. 


537 


Series  VI:  Tests  to  determine  the  effect  of  the  time  rate  of  applica- 
tion of  load  on  the  mechanical  properties  of  timber,  including  impact 
tests. 

This  is  an  exhaustive  programme  and  can  be  carried  out  only  after 
many  years  of  work;  the  results  obtained,  however,  will  be  fully 
worth  the  time  and  labor. 

Results  of  practical  value  are  expected  in  the  immediate  future 
from  Series  I,  and  these  tests  will  be  undertaken  for  the  purpose  of 
furnishing  reliable  data  within  a short  time  on  the  most  important 
species  now  in  common  use.  Specimens  for  testing  will  be  purchased 
in  the  open  market  without  special  regard  to  the  conditions  under 
which  the  trees  grew,  and  the  locality  from  which  they  came  will  be 
mentioned  in  a general  way  only,  as  “from  Berkeley  County,  S.  C.,” 
or  “from  Lewis  Count}',  Wash.”  It  is  often  impossible  to  determine 
the  botanical  species  from  an  examination  of  the  manufactured  tim- 
ber; in  many  cases  several  distinct  botanical  species  are  sold  under 
one  market  name.  In  this  series  of  tests,  therefore,  the  names  of 
species  will  be  given  only  so  far  as  practicable,  and  only  those  dis- 
tinctions will  be  drawn  which  can  be  made  by  the  engineer  or  inspector 
in  practice. 

In  the  tests  of  Series  II,  “ on  timber  collected  from  the  forest,”  there 
will  be  no  difficulty,  of  course,  in  determining  the  species.  The  work 
in  connection  with  these  tests  will  be  more  difficult  and  occupy  more 
time  than  that  of  the  former  tests,  and  will  not  begin  until  the  Bureau 
of  Forestry  is  in  a position  to  undertake  the  work  in  a thorough  man- 
ner. This  will  be  an  investigation  of  the  greatest  iiniDortance,  and 
especially  of  great  practical  value  to  the  owners  of  timber  lands.  A 
tree  is  a living  thing,  and  therefore  wood,  even  of  the  same  species, 
has  a much  greater  variation  in  strength  than  iron  or  other  metals. 
The  strength  of  iron  or  steel  depends  upon  the  manner  in  which  it  is 
manufactured,  whereas  the  strength  of  wood  depends  largely  upon  the 
conditions  under  which  it  grew.  By  noting  such  facts  as  the  density 
of  the  stand,  the  nature  of  the  forest  mixture,  the  position  of  the  tree 
in  the  forest,  and  the  character  of  the  locality  and  soil,  a relation  will 
be  obtained  between  the  strength  of  the  timber  and  the  conditions  of 
growth.  The  physical  properties  of  the  wood  also  differ  according  to 
position  in  the  tree,  and  this  must  also  be  considered.  Such  an  inves- 
tigation will  therefore  be  of  great  service  to  practical  forestry,  for  it 
will  show  under  what  conditions  the  best  quality  of  timber  is  produced. 

“The  effect  of  moisture  and  volatile  oils  on  the  strength  of  timber,” 
Series  III,  is  one  which  will  require  careful  study.  It  has  been  found 
in  former  tests  that  timber  when  moist  may  be  50  per  cent  weaker  than 
when  comparatively  dry.  All  test  material  must  therefore  be  reduced 
to  a common  degree  of  moisture  contents,  and  in  the  case  of  many 
species  the  volatile  oils  must  also  be  taken  into  account.  For  this 
purpose  a method  is  under  consideration  which  reduces  the  disks  (to 


538  YEARBOOK  OF  THE  DEPARTMENT  OF  AGRICULTURE. 


be  tested  for  moisture  contents)  to  shavings.  These  shavings  are  placed 
in  an  iron  retort  surrounded  by  a steam  jacket,  and  through  them  is 
passed  a current  of  steam  which  carries  off  the  volatile  oil  to  a con- 
denser, where  it  is  separated  from  the  water  and  weighed.  To  deter- 
mine the  total  volatile  matter,  shavings  from  the  same  disk  are  dried 
in  vacuo  until  the  water  is  driven  off,  a stream  of  dry  air  being  passed 
through  to  carry  off  the  volatile  matter.  From  the  total  volatile  mat- 
ter thus  obtained  the  volatile  oils  as  determined  by  the  first  process 
are  deducted,  the  remainder  being  the  moisture. 

Methods  of  treating  wood  with  various  preservatives  with  a view  to 
prolonging  its  life  are  now  in  common  use  and  are  becoming  of  greater 
importance  every  day.  But  little  is  yet  known  as  to  the  effect  which 
such  treatment  has  upon  the  strength  of  the  timber,  and  therefore  the 
tests  in  Series  IV  will  be  of  particular  interest.  There  is  also  much 
difference  of  opinion  about  the  effect  of  kiln-drying,  and  this  matter 
will  receive  careful  attention  in  Series  Y. 

In  Series  VI  static  tests  will  be  made  at  different  time  rates  of  appli- 
cation of  loads  on  large  timbers,  and  both  static  and  impact  tests  will 
be  made  on  small  selected  sticks,  of  the  material  and  size,  for  instance, 
used  in  carriage  manufacture. 

In  all  the  tests  made  according  to  this  general  plan  special  emphasis 
is  to  be  laid  upon  the  description  of  the  material.  There  is  a wide 
variation  in  the  quality  of  timber  of  any  one  species,  and  therefore 
investigations  Avhich  do  not  consider  the  defects  of  each  stick  tested 
have  but  little  value.  All  the  large  beams  are  photographed  on  the 
four  sides  and  both  ends,  and  after  testing,  a view  is  taken  of  the 
break.  (See  Pis.  LXIX  and  LXX.)  In  addition  to  this  a written 
description  of  each  stick  is  also  made,  and  the  imperfections,  amount 
of  sapwood,  and  rate  of  growth  are  noted. 

The  tests  are  made  at  several  stations  in  different  parts  of  the  coun- 
try, and  all  the  work  is  done  according  to  a uniform  plan  arranged  by 
the  Washington  laboratory. 


